


The Experiment

by littlemarbles



Category: Undertale (Video Game)
Genre: Cousin Incest, Non-binary Napstablook (they/them pronouns), Other, Post-Pacifist, Robot Napstablook, Robot Sex, Solo, Soul Sex
Language: English
Status: Completed
Published: 2016-06-25
Updated: 2016-06-25
Packaged: 2018-07-18 01:00:56
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,839
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7293097
Author URL: https://archiveofourown.org/users/littlemarbles/pseuds/littlemarbles
Summary: <blockquote class="userstuff">
              <p>(i wrote this forever ago so it's old and bad. read for a good laugh, i guess)</p><p>Napstablook notices an odd habit that Mettaton has, and attempts to replicate it out of curiosity.</p>
            </blockquote>





	The Experiment

This was something entirely new.

After about two weeks of living with their cousin on the surface, Napstablook began to notice some very odd things about Mettaton. He would occasionally become very excited about something, lock himself in his room for less than an hour, and then come out looking much more calm with freshly-washed hands... or, were they gloves? Either way, whatever he was doing in there required him to clean his robotic mits each time he finished. What this was, Napstablook wouldn't find out until they acquired their body that MTT _begged_  Alphys to give to them.

Not too long after Napstablook got the gist of how their pale-blue, black, and white body worked, they witnessed their cousin come home after a show... and then run into his room as if his life depended on it. He barely even had time to flash Napstablook his daily "hello" after coming home- he seemed too preoccupied fiddling with the glass plate that went over his heart container. Mettaton seemed quite energetic, judging by how quickly he ran into his room and shut the door; _**so**_ energetic, in fact, that he forgot to shut it completely, as there was a small crack that one could easily see through when up close. There was no doubt that he was in there doing whatever it was that he did when he was in that sort of mood, and this gave Napstablook the perfect opportunity to see just exactly what he did while locked away in there. Of course, they could have also asked him what he was doing, but that option didn't really cross their mind at the time.

Napstablook moved as quietly as they could through the house (as quiet as you can be with a several-hundred pound metal body) in order to get to Mettaton's room. Once there, they stood parallel to the door and peaked a single eye over the crack that Mettaton had left open. What they saw wasn't really what they were expecting, but they weren't really expecting anything whatsoever in the first place.

Mettaton was laying on his pink, glittery bed in his pink, glittery room with his hand in his pink, glittery soul container. This was one of the more... _unusual_ things that Napstablook had ever seen, but it didn't stop there. Not only was Mettaton messing around with his soul and causing it to leak the sparkling, hot-pink liquid, but he was also covering his mouth with his other hand. There really wasn't an apparent reason for this until Napstablook heard him make these odd whimpering and panting noises that were muffled by his hand. They hoped that whatever he was doing didn't hurt, but they assumed that it didn't, otherwise he wouldn't be doing it. Possibly the most unusual thing about it was the fact that Napstablook could have sworn that they heard their nickname come from their cousin's covered mouth. At first, they assumed that they'd been caught, and went to hide around the corner, but this wasn't the case. He was saying it for one reason or another, but it wasn't because they were seen.

Without any sort of warning, Mettaton arched his back, and allowed a long, lust-filled moan to slip through his fingers. His legs stretched out and twitched, his sides were covered in the same pink goo that came from his heart-shaped soul, his voice started skipping at random, and as he removed his hand from the container, it too was covered in the pink liquid. That was most likely caused him to wash up after doing... whatever it was that he just did.

Once everything was said and done, Napstablook went to the safety of their own room to ponder over what they had just witnessed. They sat down on their bed and hung their legs over the edge, crossing them in the process. For the life of them, they couldn't think of any sort of explanation for what Mettaton was doing to himself. The only conclusion Napstablook came to from what they saw was that it must've felt nice, and it also must've been something embarrassing to do to yourself- thus, why he would always do it alone in his room with the door shut. But, isn't doing something like that to your soul dangerous? Surely, there was some sort of risk to it. A monster's soul is what makes a monster a monster, after all. Maybe he needed to be alone because of how risky it was? So that he wouldn't be interrupted or distracted while doing something so dangerous? Or, was there no risk at all since his soul was oozing so much liquid, and he seemed fine right after? These questions and more floated about at random in Napstablook's head, until they finally can up with a proper way to answer them. And, to do so, they were going to do _exactly_ was Mettaton did to himself. Since their bodies were so similar, it would be the next best thing to do instead of awkwardly asking Mettaton about something that he might not want you to know about.

What's the worst that could happen?

First off, in order to conduct their experiment successfully, Napstablook had to lie on their back while in bed- just like Mettaton. In order to get accurate results, they knew that they had to do everything he did to the letter. So, naturally, this started with being in bed. This was the easiest step.

Next, Napstablook had to open up the glass plate that protected their soul. This was something that only Dr. Alphys had done to them before, but since they'd seen her do it at least a dozen times, they had no problems with opening it themself. Although, it felt a little funny to have such a crucial part of their body out in the open like that. They felt vulnerable, then again, when _didn't_ they feel that way?

The last thing Napstablook had to do was quite possibly one of the most unusual. They never really touched their heart like Mettaton did before, so they approached the action with caution. They started out by gently touching the center of it with their index finger, and immediately felt a jolt of **something**  start from their core and ripple throughout their body like a wave that tapered out at the edges. This caused Napstablook's entire body to twitch in surprise, and their breath hitched in their throat. Whatever that sensation was certainly felt unlike anything they had ever experienced before, but that wasn't a necessarily a bad thing. In all honestly, touching their soul like that, even for just a moment, felt pleasant in a way that they couldn't describe. With that in mind, they could have stopped right there at the conclusion that Mettaton really did do it just because it felt nice, but Napstablook wasn't satisfied with that. As a matter of fact, they weren't satisfied in more ways than one.

Again, Napstablook pressed a finger down on the center of their heart, but they were a bit less careful with it that time. This yielded some interesting results, as they were one-hundred percent certain that the sensation they felt from pressing it in the first time was a more intense feeling of pleasure. Their body didn't jolt as hard that time, but because they weren't covering their mouth like Mettaton was, a soft, needy moan escaped their lips. Napstablook didn't have any intentions of stopping anytime soon, so in order to keep quiet, they clasped their free hand over their mouth in a desperate attempt to not make any noise that could be heard by their cousin.

Napstablook soon became more daring with their actions, and began to roughly rub their core with two fingers. Doing so caused them quite a bit of difficulty when it came to keeping quiet. Along with this, their fingers were getting covered in copious amounts of some sort of blue, sticky fluid that came from their soul. Their legs crossed and thighs squeezed together at random, which caused their sheets to become messier than expected. They could no longer hide their moans behind their single hand, and because they weren't satisfied, all attempts at staying silent were thrown to the wind, and they allowed every pant, whine, moan, and whimper to freely cross their lips. There was just one thing missing, though- and it was a crucial part of pulling this off successfully.

From what they could recall, Mettaton was whispering Napstablook's nickname under his breath while touching himself. Though, Blooky found it a bit too weird to say their own name while doing what they were doing, so they improvised. Since there was only one Napstablook, they decided that saying Mettaton's name would be just as good.

They wished that they would have thought of that sooner.

The very moment Mettaton crossed their mind, Napstablook could just barely refrain from digging their fingers into their soul. Just the thought of him drove them wild, but they couldn't figure out why. It wasn't like they were able to think properly, anyway. Their mind was foggy, and they were too drunk off of pleasure to form any coherent thoughts. The only thing that they could really focus on was a strange feeling in their lower abdomen; it almost felt as if something was building up, and because they couldn't convince themself to stop, the feeling only intensified.

It wasn't long before they were driven over the edge after that. The touching, the thoughts, the sensation of their hands being covered in blue ooze... it was all too much. Just like their cousin, Napstablook's back arched, and they were unable to stop themself from letting out an exaggerated-sounding moan mixed with their voice skipping and glitching here and there. The only notable difference was that instead of your average sinful moan, Napstablook actually called out Mettaton's name, and their voice skipped on each syllable.

By the time they were completely finished, Napstablook was an absolute mess. They were still panting, their hand was coated in blue ooze, their hair had somehow gotten knots in it, and their thoughts were still mindlessly floating about in their head. They were exhausted, to say the least. Napstablook couldn't even bring themself to get up and wash their hands. They were also too tired to notice that their door was left wide-open, allowing Mettaton to watch in silent shock and disbelief. He would have _never_ expected his sweet, innocent little cousin to do something like that- **especially** while thinking about him in such a way. He almost wanted to spoil their fun by saying something, but that would have been cruel. Maybe next time, he could help them out a bit? That's certainly be a fun idea to toy around with. For now, Mettaton just walked away as if nothing ever happened. That was the most sensible thing to do, after all.

At least Napstablook finally got the satisfaction they craved in the first place.

**Author's Note:**

> I am  
> so sorry.
> 
> This is my first of (hopefully) many fics on this site. Let me know what you think!


End file.
